1. Field of the Invention
This invention relates to a combination axle-torsion beam type suspension for use such as in the rear suspension of an automobile and a method for the production thereof.
2. Description of the Prior Art
The recent automobiles have been urging satisfaction of increasingly rigid demands for lightening weight and simplifying structure of the vehicle and for lowering cost of the manufacture by such reasons as the intensifying competition in price and the exacting necessity for preserving resources and saving energy. The suspensions in the automobiles are not exempted from this trend.
To fulfill these demands, the recent automobiles have come to adopt a combination axle-torsion beam type suspension which is adapted to interconnect the axles of laterally opposite wheels with one beam (as disclosed in JP-A-03-224,812 and shown in the "Automobile Engineering," Volume 11 titled "Steering Suspension," pp. 102 and 103, published by Sankaido, for example).
The torsion beam type suspension which is used in the rear suspension has wheel supporting members attached one each to the opposite ends of a torsion beam having a cross section of the shape of an inverted letter U and trailing arms rigidly joined as by welding to the opposite end parts and assigns the intermediate part between the trailing arms as a member destined to be twisted.
This torsion beam is vested with a structure capable of lowering exclusively the torsional rigidity of the torsion beam without lowering the bending rigidity thereof, namely a cross-sectional structure having the lower end side of the shape of an inverted letter U left open (hereinafter referred to as "open inverted U cross-sectional structure"), for the purpose of facilitating the motion of the automobile body in the vertical direction while the positioning of the automobile body in the lateral and the longitudinal direction is in progress. At times, it may be furnished with a stabilizer for the purpose of enervating the rolling which is generated by the centrifugal force while the automobile is in the process of making a curve in travel.
In this suspension, the trailing arms and the torsion beam immediately move vertically and generate no torsion when the laterally opposite wheels produce strokes of an equal amount in the same direction relative to the automobile body. When the automobile body is tilted under the centrifugal force exerted thereon and the laterally opposite wheels consequently execute strokes in the reverse direction relative to the automobile body as when the automobile makes a turn, for example, the torsion beam is induced to generate torsion. This torsion is positively utilized for the function of the suspension.
When the laterally opposite wheels execute a stroke in the reverse direction as described above, the torsion beam is twisted and induced to generate a torsional reaction proportionate to the torsional rigidity of the torsion beam and the automobile body is consequently tilted until the resultant force between this torsional reaction and the laterally opposite spring reactions equals the force tending to tilt the automobile body.
The adjustment of this tilt of the automobile body, namely the so-called stabilizer effect, therefore, can be attained by adjusting the torsional rigidity of the torsion beam. The torsion beam type suspension, therefore, may well be regarded as a suspension which has a stabilizer integrated with an axle serving the purpose of positioning the laterally opposite wheels.
Incidentally, the stabilizer effect has the optimum strength of its own, depending on the characterizing features of the relevant automobile. For the purpose of adjusting this stabilizer effect, it is desirable to alter suitably the torsional rigidity of the torsion beam depending to the kind of automobile.
When the torsion beam which is formed of a beam having a cross section of the shape of an inverted letter U as described above is used, it is not easy to alter or adjust the torsional rigidity without noticeably varying the cross-sectional size of the torsion beam. Because of the restriction imposed on the peripheral space, it is difficult to manufacture the torsion beam in a structure capable of offering the optimum rigidity.
For the purpose of enabling the torsion beam to attain required adjustment of the torsional rigidity, therefore, the torsion beam is provided additionally with a rodlike or a tubular stabilizer. Thus, this torsion beam is at a disadvantage in increasing the number of component parts and the weight of its own.
Since the suspension of this kind must be completed so that the spindle thereof may acquire prescribed toe-in angle (0.5 degree, for example) and camber angle (1 degree, for example) and the surface for mounting the brake may possess prescribed accuracy of runout, the parallelism between the spindle and the surface for mounting the spindle or the surface for mounting the brake, the difference in height between these two surfaces, and the tilt of the axle demand unusually exacting accuracy. For this reason, the hole for forced insertion of the spindle and the surface for mounting the brake are processed by machining after the end plate has been joined to the torsion beam by welding and before the spindle is finally inserted into the end plate under pressure.
When the end plate is processed by machining, therefore, the torsion beam of a usually great length must be wholly set in place preparatorily on a machine. Thus, the equipment for machining inevitably becomes voluminous and the cost of equipment and the cost of production are proportionately high.